settings: wifi priorities

Added the ability of graphically set the priority of any of the saved Wi-Fi networks
through Settings -> Wi-Fi -> Saved networks

Require: http://review.cyanogenmod.org/100830
         http://review.cyanogenmod.org/100831



JIRA: CML-118

Change-Id: Id535a7bd8865897bfed0570675ef837a5d410779
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>